The Book of Sorrows

You'll need to read The Book of the Dun Cow, a story about a war between Good and Evil fought by talking animals, before picking up this one. The sequel follows the aftermath of that battle, but it's not the rebuilding of the community readers might expect; darkness, death, and destruction feature throughout. If a book has never made you cry, this might be the one to change that. Never before has a book been so aptly titled, and it left me in a depressive funk for weeks. Still, beautifully written and worth reading. (Ignore the third book, it's nothing like the first two and was obviously written decades later as a cash grab.)